Conventionally, there is known a four-wheel-drive vehicle in which a driving force of a drive source is normally transmitted to a front wheel side and a driving force that is required by the vehicle according to its driving conditions is transmitted to a rear wheel side via a torque coupling which can change a torque transmission capacity (for example, refer to Patent Document 1).
A four-wheel-drive vehicle described in Patent Document 1 has a torque coupling which can change a torque transmission capacity at a rear wheel side of a propeller shaft and a switching mechanism such as a dog clutch which can engage and disengage the transmission of torque between an output shaft of a transfer and the propeller shaft. Then, when a two-wheel drive in which only front wheels are driven is engaged in the vehicle, the transmission of torque is cut off at the front and rear of the propeller shaft so as to prevent the rotation of the propeller shaft while the vehicle is running in two-wheel drive, whereby the sliding resistance and oil agitation loss associated with the rotation of the propeller shaft are reduced so as to increase the fuel economy.